Dungeon Master’s Guide, hardback core rulebook for D&D 3rd edition, by Monte Cook, Skip Williams, and Jonathan Tweet.
“Worlds of Inspiration!
You’ve got the Dungeons & Dragons Player’s Handbook, but you need more – you’e the Dungeon Master, and it’s up to you to create adventures and worlds for your friends’ characters to experience, explore and conquer.
This book contains everything you need – from special high-level classes to magic items, artifacts and more! You’re the Dungeon Master, and all the Dungeons & Dragons secrets are yours!”